Update API template to use new Problem helpers in error handler

[DamianEdwards]

Relies on #8537

Update error handler action method to use new problem helper method #8537:

[Route("/error")]
public ActionResult<ProblemDetails> HandleError()
{
    return new ProblemDetails
   {
        Title = "An error occurred while processing your request.",
        Status = 500
    };
}

[isaacrlevin]

@mkArtakMSFT this good to take now after latest PR?

[mkArtakMSFT]

I'm not sure I understand you question, @isaac2004.
Are you asking whether you can take this and send a PR for it? If so - that'll be amazing. We'll happily review a PR for this.

[ryanbrandenburg]

#8537 is still open. Has it actually been completed and we just missed updating it? Or does this issue not actually rely on that one somehow?

[mkArtakMSFT]

@ryanbrandenburg you're right. The referenced issues would make this much easier to accomplish. So that should come first.

[pranavkm]

Unblocked now

[mkArtakMSFT]

Moving to 5.0 after discussing this with @glennc and @pranavkm